A loudspeaker is a transducer that produces sound in response to an electrical audio signal input. The vast majority of loudspeakers in use today are electromagnetic transducers. Referred to as dynamic loudspeakers, that class has essentially remained unchanged since the 1920's. Typically, a linear motor, such as an electromagnetic or electrostatic motor, actuates a diaphragm, which causes sound waves to be emitted by the speaker.
More recently, a new class of mechanical-to-acoustical transducers has been developed. Those transducers may have an actuator that may be coupled to an edge of a speaker diaphragm or diaphragm that may then be anchored and spaced from the actuator. In such transducers, the actuator is typically a piezoelectric actuator. Mechanical motion of the actuator is translated into movement of the diaphragm, generally in a direction that is transverse to the direction of motion of the actuator. The diaphragm radiates acoustic energy. Mechanical-to-acoustical transducers are exemplified in each of U.S. Pat. Nos. 6,720,708 and 7,038,356.
A problem with this new class of mechanical-to-acoustical transducers is durability. For example, unlike most dynamic loudspeakers, the diaphragm is not completely housed in an enclosure. Being exposed to the environment, means the diaphragm is vulnerable to normal wear and tear, such as bumping into and against other objects in a room. Collisions with the diaphragm may bend the diaphragm to the point of cracking or breaking.